Tandem Palladium Catalysis for Rapid Construction of 3,4‐Fused Tricyclic Indoles.

Tandem catalysis, the use of a single catalyst to promote two or more mechanistically distinct cycles in one pot to assemble complex organic molecules, is an attractive target. In this paper, we report a reductant‐triggered tandem palladium catalysis process that rapidly assembles 3,4‐fused tricyclic indoles from three readily available starting materials. This tandem process involves a Pd0‐catalyzed in situ coupling/cyclization/Michael addition reaction to install simultaneously two functional groups at the C4 and the C3 positions of indoles. This is followed by a Pd0‐catalyzed intramolecular cyclization which builds a seven‐membered C4, C3‐bridge. Sodium formate is used to trigger the necessary switching between the palladium catalysed reactions. [ABSTRACT FROM AUTHOR]